This invention relates to a process for the separation of CO.sub.2 from CO.sub.2 -containing gases, especially stack or flue gases and/or blast furnace gases, by scrubbing with a physical scrubbing medium which is thereafter regenerated to remove CO.sub.2, and is then recycled into the scrubbing stage.
Several methods are known for obtaining CO.sub.2 from gaseous mixtures. Chemical and physical scrubbing operations, as well as adsorptive separating methods have distinguished themselves as the important processes. Important chemical scrubbing operations include, for example, the NH.sub.3 or monoethanolamine (MEA) scrubbing processes, whereas the methanol scrubbing process conducted at low temperatures is important as a physical scrubbing operation. Adsorptive removal of CO.sub.2 from gaseous mixtures can be effected with the aid of activated carbon or a molecular sieve. Another possibility for separating CO.sub.2 from gaseous mixtures is the regenerator method employing the periodic application of a vacuum to purge the regenerator of CO.sub.2.
Though the technology of removing CO.sub.2 from industrial gases is indeed very old, all the conventional processes exhibit one or more disadvantages. For example, the chemical scrubbing methods require for regeneration a very high thermal input, in the form of low-pressure steam (.gtoreq.2.5 bar), for example, and such methods initially yield a water-saturated gas which, due to danger of corrosion, must be dried before being further compressed (generally to 140 bar). Physical scrubbing with methanol, as the absorbent, due to the high vapor pressure of methanol may result in very high losses of scrubbing medium. In this process, the stack gas, at ambient pressure, would either have to be compressed to high pressures, or the process would have to be conducted under extremely low temperatures to maintain losses of methanol within economical limits. However, both measures entail excessive costs in energy. Finally, the regenerator process yields a gas having too high a proportion of N.sub.2 which would have to be subsequently separated at high expense in order to obtain sufficiently pure CO.sub.2.